This invention relates to cyanoacrylate compositions and methods of detecting cure of the cyanoacrylate compositions using luminescent dyes.
Cyanoacrylate adhesives are known for their fast adhesion and ability to bond a wide variety of substrates. They are marketed as xe2x80x9csuper gluexe2x80x9d type adhesives. They are useful as an all-purpose adhesive since they are a single component adhesive, very economical as only a small amount will do, and generally do not require any equipment to effectuate curing. However, in some instances there is a tendency for adhesion failure to occur, particularly when the end user does not know when the adhesive has fully cured.
Fluorescing agents have previously been incorporated into curable compositions to provide a non-destructive method of inspection such as identifying cured films, and ensuring proper coating of the composition on an article. These fluorescing agents are typically used in UV/VIS (ultraviolet/visible) curable compositions. Most cyanoacrylate compositions do not require actinic radiation to effect cure.
Other dyes have been incorporated into polymeric compositions generally to color the composition rather than as a cure indicator as there is no color change associated therewith.
U.S. Pat. No. 6,017,983 (Gilleo) appears to refer to the use of a diazo dye that is believed to form a salt or complex with acid anhydrides, which acts as a color indicator for particular anhydride/epoxy resin thermoset adhesives. The resulting salt or complex is reported to produce a chromophoric shift in the dye which is indicative of the amount of acid anhydride present, and hence, the degree of cure. As the epoxy resin cures, the amount of acid anhydride diminishes thus producing a color change. This system appears to be limited to acid anhydride hardeners used to cure epoxy resins.
U.S. Pat. No. 5,302,627 (Field) reports the addition of a dye to UV radiation curable silicone-containing polymeric compositions that contain photoinitiators. Upon exposure to UV radiation, the silicone-containing polymeric composition undergoes a color change indicating that the composition has cured. The dyes used include an anthraquinone dye having a Color Index Solvent Blue 104, 1-hydroxy-4-[(methylphenyl)amino]-9,10-anthracenedione, and an azo dye mixture of azo benzene azo naphthyl benzene amine alkyl/alkoxy derivatives having a Color Index Solvent Blue 99, and azo benzene azo naphthyl benzene amine alkyl derivatives having a Color Index Solvent Red 166. Large amounts of the dye, greater than 30 ppm based on the weight of the composition, are reported to inhibit cure.
Notwithstanding the state of the technology, it would be desirable to provide a cyanoacrylate composition that has a built in method of detection or is xe2x80x9cself-indicatingxe2x80x9d when cure has been achieved.
In a first aspect, the present invention is directed to a cyanoacrylate composition having a cure indicator. The composition includes a cyanoacrylate component; and a dye dissolved in the cyanoacrylate component to provide a solution having a first color, where upon curing of the cyanoacrylate component, the resultant cured composition has a second color.
In a second aspect, the present invention is directed to a cyanoacrylate composition. The composition includes a cyanoacrylate component; a member selected from the group consisting of accelerators, fillers, opacifiers, thickeners, viscosity modifiers, inhibitors, thixotropy conferring agents, and combinations thereof; and a fluorescent dye in an amount of about 100 to 400 ppm based on an amount of the cyanoacrylate component which imparts a first non-fluorescent color to the cyanoacrylate component. The fluorescent dye is selected from fluorescein, dibromofluorescein, diiodofluorescein, tetrabromofluorescein, tetrabromotetrachlorofluorescein, and combinations thereof. Upon curing, the cured composition exhibits a fluorescent color.
In a third aspect, the present invention is directed to a method of making a cyanoacrylate composition having a cure indicator. The method includes the steps of providing a cyanoacrylate component; providing a dye; substantially dissolving the dye in the cyanoacrylate component to form a cyanoacrylate component having a first color; and curing the cyanoacrylate component to form a cured composition having a second color.
In a fourth aspect, the present invention is directed to a method of curing a polymeric composition. This method includes the steps of providing a cyanoacrylate component; providing a cure indicator; dissolving the cure indicator in the cyanoacrylate component to form a visually color-less solution; exposing the visually color-less solution to conditions appropriate to effect cure; and detecting fluorescence of the cure indicator as an indication of substantial cure.
In a fifth aspect, the present invention is directed to a method of detecting cure of an adhesive. The detection method includes the steps of providing a first article and a second article; providing, on a surface of the first article, an adhesive; contacting a surface of the second article to the surface of the first article having the adhesive thereon; exposing the first and second articles to conditions appropriate to effect cure; and detecting fluorescence of the cured adhesive. The adhesive, in its uncured state, includes a visually colorless solution of a cyanoacrylate component and a dye.
Preferably, in the present invention, the fluorescent dye is selected from fluorescein, dibromofluorescein, diiodofluorescein, tetrabromofluorescein, and tetrabromotetrachlorofluorescein. Preferably, the dyes are present in an amount sufficient to impart observable color when the composition is cured, preferably about 50 to about 1000 ppm, and more preferably, about 100 to about 400 ppm based on an amount of the cyanoacrylate monomer.
The present invention is directed to a cyanoacrylate composition, having a cure indicator. That is, the cyanoacrylate composition is xe2x80x9cself-indicatingxe2x80x9d with respect to its ability to allow the end user to visually inspect the composition to determine whether, and the extent to which, cure has occurred. The composition includes a cyanoacrylate component, and a dye dissolved in the cyanoacrylate component. The cyanoacrylate composition has an initial color, oftentimes colorless or substantially so to the naked eye, and when cured, the cured cyanoacrylate composition has a different or second color including fluorescence. Observation of the different or second color is indicative that cure has occurred and the extent of the color change can be used to determine the degree of cure that has occurred. The cured cyanoacrylate composition undergoes a color change and glows, i.e., luminesces, under black light, thereby confirming cure of the cyanoacrylate composition.
The cyanoacrylate component useful in the present invention includes cyanoacrylate monomers, such as those represented by the structure: 
wherein R1 is selected from C1-16 alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aralkyl, aryl, allyl and haloalkyl groups. Preferably, the cyanoacrylate monomer is selected from methyl cyanoacrylate, ethyl-2-cyanoacrylate, propyl cyanoacrylates, butyl cyanoacrylates (such as n-butyl-2-cyanoacrylate), octyl cyanoacrylates, allyl cyanoacrylate, xcex2-methoxyethyl cyanoacrylate and combinations thereof. A particularly desirable cyanoacrylate monomer is ethyl-2-cyanoacrylate. The cyanoacrylate component should be included in the compositions in an amount within the range of about 50 wt to about 99.8 wt. %, preferably about 90 wt. % to about 98 wt. %.
The compositions of the present invention may also contain additives such as stabilizers, accelerators, fillers, opacifiers, thickeners, viscosity modifiers, inhibitors, thixotrophy conferring agents, and combinations thereof. These additives are known to those of skill in the art. The cyanoacrylate monomers are preferably stabilized using acid stabilizers of the Lewis or protonic types although combinations of nonvolatile sulfonic acids with gaseous stabilizers such as NO, SO2, SO3, BF3, and HF can provide a synergistic effect. A preferred stabilizer system for the present invention comprises methane sulfonic acid (xe2x80x9cMSAxe2x80x9d) and SO2. Preferably, the amount of MSA is about 5 to about 25 ppm and a preferred amount of SO2 is about 2 to about 30 ppm based on the amount of the cyanoacrylate monomer. More preferably, BF3, another acidic gaseous stabilizer, may also be added in amounts of about 5 ppm to about 50 ppm based on the amount of the cyanoacrylate monomer. The combination of the cyanoacrylate monomer and the additives will be referred to herein as a cyanoacrylate component.
The cyanoacrylate components of the present invention are typically curable using an anionic mechanism utilizing free radical generation. The layer of moisture inherently adsorbed on the surfaces of virtually all materials is sufficient to initiate polymerization of the cyanoacrylate component. The hydroxyl groups of the water molecules effectively act to initiate polymerization as carbanions are generated at a rapid rate. The polymerization reaction will continue until all available monomer is consumed or until growth is inhibited by an acidic species.
Fluorescent dyes which are useful in the present invention are substantially soluble in and non-reactive with the cyanoacrylate component and do not adversely affect the curing properties of the monomer. Fluorescent dyes which adversely affect the storage stability of the cyanoacrylate component are undesirable as well, in particular, those fluorescent dyes having a free nitrogen render the cyanoacrylate components unstable. The preferred compositions of the present invention were found to exhibit good stability having a shelf life of greater than about 1 year at or about room temperature. Shelf life was determined by heating the compositions in glass tubes at 82xc2x0 C.
The dyes suitable for use in accordance with the present invention are present in an amount sufficient to impart observable color when the composition is cured, preferably about 50 to about 1000 ppm, and more preferably about 100 to about 400 ppm based on an amount of the cyanoacrylate monomer.
Those dyes classified as xanthenes and anthraquinones are preferred, particularly those which can be readily solubilized in the cyanoacrylate component in the chosen amount and do not adversely affect the curing of the monomer. Xanthenes are characterized by the following structure: 
Fluorans are a preferred class of xanthene dyes suitable for use in the present invention. Particularly preferred fluorans comprise fluorescein (DandC Yellow #7), dibromofluorescein (DandC Orange #5), diiodofluorescein (DandC Orange #10), tetrabromofluorescein (DandC Red #21), and tetrabromotetrachlorofluorescein (DandC Red #27, also known as Pylam Red #27). Anthraquinone dyes are characterized by the following structure: 
Preferred anthraquinone dyes are 7,16-dichloro-6,15-dihydro-5,9,14,18-anthrazine-tetrone (DandC Blue #9), the disodium salt of 2,2xe2x80x2-[(9,10-dihydro-9,10-dioxo-1,4-anthracenediyl)diimino]bis-[5-methylbenzenesulfonic acid (DandC Green #5), 1,4-bis(4xe2x80x2-methylanilino)anthraquinone (DandC Green #6), and 1-hydroxy-4-(4-methylanilino)anthraquinone (DandC Violet #2). DandC is the category of dyes and pigments considered safe for drugs and cosmetics when in contact with mucous membranes or when ingested, as determined by the U.S. Food and Drug Administration.
The dye is substantially dissolved in the cyanoacrylate component thereby producing a visually color-free composition, or the composition may have a faint color associated therewith. The composition is typically a liquid but its viscosity may be modified to an extent to reach a non-flowable gel depending on the amount of thickeners added to adjust the viscosity of the composition. The viscosity range of the compositions of the present invention may be from about 5 cps to a non-flowable gel. Unexpectedly, when the dye is dissolved in the cyanoacrylate component of the present invention, there is no initial fluorescence and little to no color; however, upon exposure to conditions appropriate for cure, the cured composition fluoresces, as seen under black light, and undergoes a visible color change. The visible color change may be from substantially colorless to red/pink or from fluorescent yellow/green to substantially colorless. The color change and/or change in fluorescence provides an advantageous cure indicator for the end user to readily determine without the use of sophisticated and expensive detection equipment when the adhesive has substantially cured.
The following examples describe the preparation and use of the colored cyanoacrylate compositions of the present invention. These examples are presented for the purpose of further illustrating and explaining the invention, and are not to be taken as limiting the scope of the invention.